1. Field of the Invention
This invention relates to a process for effecting isomerization of an aromatic C.sub.8 mixture comprising ethylbenzene and xylene in the presence of a specified crystalline aluminosilicate zeolite catalyst characterized by a crystalline size of at least about 1 micron. The catalyst has associated with it platinum and a Group IIA metal. The invention also relates to a method of making a catalyst.
2. Description of the Prior Art
Xylene isomerization in the presence of a catalyst is well known to the art. U.S. Pat. No. 3,856,872 (Morrison) dated Dec. 24, 1974, shows a method of converting ethylbenzene over an active acid catalyst typified by zeolite ZSM-5. Ethylbenzene disproportionates to benzene and diethylbenzene which are readily separated from xylene by the distillation equipment needed in the loop to remove byproducts. It is recognized that rate of disproportionation of ethylbenzene is related to the rate of conversion of xylene into other compounds, e.g., by disproportionation. See also Burress, U.S. Pat. No. 3,856,873 which also describes reaction of C.sub.8 aromatics over ZSM-5 and shows effects of various temperatures up to 950.degree. F. in the absence of metal catalyst and in the absence of hydrogen. In the presence of the catalyst and operating at these higher temperatures, the transalkylation route for xylene losses is reduced; however, xylene losses via the disproportionation route is increased. The xylene loss byproducts are mostly trimethylbenzene, ethyl-xylene and C.sub.9 + aromatics.
U.S. Pat. No. 4,098,837 (Chu) dated July 4, 1978, discloses a zeolite catalyst which incorporates phosphorus and one or more metals, including magnesium, in an effort to elicit a greater para-xylene content from the feed material. U.S. Pat. No. 4,159,282 (Olson et al) dated June 26, 1979, discloses xylene isomerization with a crystalline zeolite catalyst having a crystal size of at least 1 micron. The original alkaline metal of the zeolite may be replaced by ion exchange with suitable ions of Groups IB to VIII. A second metal, e.g., magnesium, may be combined with the zeolite.
U.S. Pat. No. 4,163,028 (Tabak et al) dated July 31, 1979, discloses xylene isomerization and ethylbenzene conversion at temperatures of 800.degree. F. or higher with ZSM-5 or very high silica/alumina ratio whereby the acid activity is reduced.
U.S. Pat. No. 4,278,565 (Chen et al) dated July 14, 1981, discloses a zeolite catalyst having a crystalline size greater than 1 micron, e.g., HZSM-5C. Three metals are incorporated onto this catalyst: a Group IIB metal, a Group VIII metal and magnesium.